Regulation of acetyl-coA carboxylase: properties of coA activation of acetyl-coA carboxylase.

Acetyl-CoA carboxylase [acetyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] is activated by physiological concentrations of CoA. The CoA concentration dependency of this activation is sigmoidal; below 60 microM there is little or no activation, but the activation observed between 60 and 120 microM indicates that small changes in the concentration of CoA can cause significant changes in carboxylase activity. CoA activation of acetyl-CoA crboxylase accompanies polymerization of acetyl-CoA carboxylase. However, the binding site for CoA appears to be different from that of citrate. In contrast to citrate activation, which changes only the Vmax of the reaction, CoA activation of carboxylase results in polymeric forms with a lower Km for acetyl-CoA. The Km for acetyl-CoA is 0.4 mM in the control enzyme, whereas that of the CoA-activated enzyme is as low as 4 microM. The Km for ATP was not changed. Derivatives of CoA were not effective in activating the carboxylase, indicating that the CoA effect is specific. Arguments are presented that CoA could be a physiologically significant positive effector of the carboxylase.